The present invention relates to a light emitting/receiving element for an optical pickup apparatus. More particularly, the present invention concerns a light emitting/receiving element incorporated in an optical pickup apparatus in which a second semiconductor substrate provided with a laser diode and a monitoring light receptor is disposed at a position higher than a first semiconductor substrate provided with a light receptor. It should be noted that the heightwise direction referred to hereunder means a direction which is perpendicular to a metallic radiator plate and on which a protruded section is formed.
As a related light emitting/receiving element for an optical pickup apparatus, a holographic optical element (HOE) unit used in an optical pickup apparatus such as a CD player is shown in FIG. 6. This light emitting/receiving element 101 is so constructed that a light receptor (photodiode) 103 and a circuit for calculating a focus error signal or the like are formed on an IC chip (first semiconductor substrate) 102, and a submount (second semiconductor substrate) 105 with a monitoring light receptor (PIN photodiode) 104 formed thereon and a laser diode (light emitter) 106 are superposed on the IC chip 102. The reason for superposing the submount 105 and the laser diode 106 on the IC chip 102 in this manner is to dispose the laser diode 106 at a predetermined height with respect to the IC chip 102 in view of the relationship with an HOE optical system, and to make return light from a recording medium incident upon the light receptor 103 on the IC chip 102. It should be noted that, in FIG. 6, reference numeral 107 denotes an electrode, numeral 108 denotes a bonding wire, and numeral 109 denotes Ag paste.
The laser light emitted from the front side of the laser diode 106 is reflected by a reflecting mirror, is focused by a lens, and forms an image as a spot on a recording medium such as a CD. The return light from the recording medium is reflected by the reflecting mirror, is diffracted by an optical element, and is incident upon the light receptor 103 on the IC chip 102. The laser light emitted from the rear side of the laser diode 106 is incident upon the monitoring light receptor 104 on the submount 105 so as to be used for monitoring.
However, with the aforementioned light emitting/receiving element 101, there has been a drawback in that the size of the IC chip 102 becomes large since the submount 105 and the laser diode 106 are superposed on the IC chip 102. Namely, despite the fact that the area of the IC chip 102 where the submount 105 is mounted is an area which is functionally unnecessary as the IC chip 102, the size of the IC chip 102 becomes large by the portion of this mounting area for the sole purpose of superposing the laser diode 106 thereon. For this reason, the number of chips which can be manufactured from one semiconductor wafer is reduced, thereby increasing the manufacturing cost.
In addition, since the laser diode 106 radiates heat, there is a need to efficiently transmit this heat to another member so as to speedily dissipate the heat. With the aforementioned light emitting/receiving element 101, however, since the IC chip 102 with the submount 105 and the laser diode 106 superposed thereon is mounted on a lead frame of the HOE unit, it is necessary to adopt a heat radiating means such as by widening the ground (GND) terminal of the lead frame in terms of its shape so as to increase its heat radiating area or by causing this GND terminal to abut against a frame of the optical pickup apparatus so as to dissipate the heat to the frame. The structure for such a purpose is complicated, which increases the manufacturing cost.
The object of the invention is to provide a light emitting/receiving element for an optical pickup apparatus which makes it possible to reduce the size of the IC chip and obtain a satisfactory heat radiation characteristic with a simple structure.
In order to achieve the above object, according to the present invention, a flat plate section and a protruded section are formed in a metallic radiator plate. Then a first semiconductor substrate with a light receptor mounted thereon is disposed on the flat plate section of the metallic radiator plate, and a second semiconductor substrate with a laser diode and a monitoring light receptor mounted thereon is disposed on the protruded section of the metallic radiator plate. Accordingly, it is unnecessary to mount the second semiconductor substrate on the first semiconductor substrate, so that the first semiconductor substrate can be made small. For this reason, it is possible to increase the number of first semiconductor substrates which can be manufactured from one semiconductor wafer, thereby making it possible to reduce the manufacturing cost of the first semiconductor substrate. In addition, since the first semiconductor substrate can be made small, the optical pickup apparatus into which the light emitting/receiving element is incorporated can be made compact and lightweight.
In addition, since the heat generated by the laser diode can be transmitted to the metallic radiator plate so as to be dissipated, the heat radiation characteristic of the laser diode can be improved. Moreover, since the structure for heat radiation is made simple, the manufacturing cost can be lowered. Furthermore, since it is possible not to use the base substrate as a heat radiator, it becomes possible to use a resin substrate which is low in cost and on which a complicated circuit can be formed.
Alternatively, a recessed portion and a flat plate section may be formed in a metallic radiator plate. Then, a first semiconductor substrate with a light receptor mounted thereon is disposed in the recessed portion of the metallic radiator plate, and a second semiconductor substrate with a laser diode and a monitoring light receptor mounted thereon is disposed on the flat plate section of the metallic radiator plate. Therefore, in the same way as the above configuration, the first semiconductor substrate can be made small, and it is possible to reduce the manufacturing cost of the first semiconductor substrate. At the same time, the optical pickup apparatus into which the light emitting/receiving element is incorporated can be made compact and lightweight. In addition, the heat radiation characteristic of the laser diode can be improved, the structure for heat radiation is made simple, thereby making it possible to lower the manufacturing cost. Furthermore, the use of a resin substrate as the base substrate is permitted. In addition, since the second semiconductor substrate for mounting the laser diode thereon is disposed on the flat plate section of the metallic radiator plate, the arrangement facilitates the setting of the heightwise position of the laser diode with high accuracy.